Method for silicide formation

ABSTRACT

Embodiments of the present disclosure include contact structures and methods of forming the same. An embodiment is a method of forming a semiconductor device, the method including forming a contact region over a substrate, forming a dielectric layer over the contact region and the substrate, and forming an opening through the dielectric layer to expose a portion of the contact region. The method further includes forming a metal-silicide layer on the exposed portion of the contact region and along sidewalls of the opening; and filling the opening with a conductive material to form a conductive plug in the dielectric layer, the conductive plug being electrically coupled to the contact region.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.14/321,366, entitled “Method for Silicide Formation,” filed on Jul. 1,2014, which application is hereby incorporated herein by reference.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as personal computers, cell phones, digital cameras, and otherelectronic equipment, as examples. Semiconductor devices are typicallyfabricated by sequentially depositing insulating or dielectric layers,conductive layers, and semiconductive layers of material over asemiconductor substrate, and patterning the various material layersusing lithography to form circuit components and elements thereon.

The semiconductor industry continues to improve the integration densityof various electronic components (e.g., transistors, diodes, resistors,capacitors, etc.) by continual reductions in minimum feature size, whichallow more components to be integrated into a given area.

Conductive materials such as metals or semiconductors are used insemiconductor devices for making electrical connections for theintegrated circuits. As devices have decreased in size, the requirementsfor the conductors and insulators have changed.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a cross-sectional view of a semiconductor device inaccordance with some embodiments.

FIGS. 2A through 2G are cross-sectional views of intermediate stages inthe manufacturing of a semiconductor device in accordance with someembodiments.

FIG. 3 illustrates a cross-sectional view of another semiconductordevice in accordance with some embodiments.

FIG. 4 illustrates a process flow diagram of the process shown in FIGS.2A through 2G in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

In general terms, using embodiments of the present disclosure,semiconductor devices can leverage a low resistance silicide contactwith improved process stability. In particular, the present disclosureforms the silicide in the contact opening after the contact opening isformed rather than forming the silicide before the contact is formed. Inthis process, a capping layer is formed inside the contact opening and ametal layer is formed over the capping layer. These layers are thenannealed to form the silicide layer. By forming the capping layer afterthe contact opening is formed, the capping layer properties are notaffected by the contact opening etching process, the dielectric layerformation, or any other processes performed before the capping layerformation. This improves the processing window for the capping layerformation and also improves the process stability for the contactformation. In addition, the capping layer can repair damage caused bythe etching of the contact opening.

FIG. 1 illustrates a cross-sectional view of a semiconductor device 100in accordance with some embodiments. The semiconductor device 100includes a substrate 20, active or passive devices 22, a contact layer24, a dielectric layer 26, and a contact structure 50. The contactstructure includes a metal-silicide layer 40, an unreacted metal layer32′, a glue layer 34, and a conductive plug 42′.

The substrate 20 may be a part of a wafer and may include asemiconductor material such as silicon, germanium, diamond, or the like.Alternatively, compound materials such as silicon germanium, siliconcarbide, gallium arsenic, indium arsenide, indium phosphide, silicongermanium carbide, gallium arsenic phosphide, gallium indium phosphide,combinations of these, and the like, may also be used. Additionally, thesubstrate 20 may comprise a silicon-on-insulator (SOI) substrate.Generally, an SOI substrate comprises a layer of a semiconductormaterial such as epitaxial silicon, germanium, silicon germanium, SOI,silicon germanium on insulator (SGOI), or combinations thereof. Thesubstrate 20 may be doped with a p-type dopant, such as boron, aluminum,gallium, or the like, although the substrate may alternatively be dopedwith an n-type dopant, as is known in the art.

The substrate 20 may include active and passive devices 22. As one ofordinary skill in the art will recognize, a wide variety of devices suchas transistors, capacitors, resistors, combinations of these, and thelike may be used to generate the structural and functional requirementsof the design for the semiconductor device 100. The active and passivedevices 22 may be formed using any suitable methods. Only a portion ofthe substrate 20 is illustrated in the figures, as this is sufficient tofully describe the illustrative embodiments.

A contact layer 24 is formed over the substrate 20. The contact layer 24may include a doped region over the substrate 20. In some embodiments,the contact layer 24 is formed directly on or in a top surface of thesubstrate 20. The dielectric layer 26 is formed over the contact layer24. The dielectric layer 26 may be formed of oxides such as siliconoxide, low-k dielectrics, polymers, the like, or a combination thereof.

The contact structure 50 is formed to extend through the dielectriclayer 26 to the contact layer 24. The contact structure 50 may be formedin an opening in the dielectric layer 26 (see FIGS. 2A through 2Fdiscussed below). The contact structure 50 includes the metal-silicidelayer 40 directly adjoining the contact layer 24 and the dielectriclayer 26. The metal-silicide layer 40 provides a low resistance contactto the contact layer 24 and good adhesion to the contact layer 24. Insome embodiments, the metal-silicide layer 40 extends alongsubstantially the entire sidewall of the contact structure 50 from thecontact layer 24 to a top surface 26A of the dielectric layer 26. Themetal-silicide layer 40 may have a surface of the portion 40A thatextends lower than a top surface 24A of the contact layer 24 as some ofthe contact layer 24 may be consumed during the silicidation process toform the metal-silicide layer 40.

The unreacted metal layer 32′ is on the metal-silicide layer 40. Theunreacted metal layer 32′ is the metal layer that was not consumedduring the formation of the metal-silicide layer 40. In someembodiments, the unreacted metal layer 32′ is not present assubstantially the entire metal layer is consumed during the formation ofthe metal-silicide layer 40. The glue layer 34 is formed on theunreacted metal layer 32′. The glue layer 34 improves the adhesionbetween the subsequently formed conductive plug 42′ and also preventsoxidation of the unreacted metal layer 32′ (also the metal layer 32before silicidation process in, for example, FIG. 2D).

The conductive plug 42′ is formed on the glue layer 34 and maysubstantially fill the remaining portion of the opening in thedielectric layer 26. In some embodiments, the conductive plug 42′ has atop surface 42A that is substantially coplanar with the top surface 26Aof the dielectric layer 26.

FIGS. 2A through 2G are cross-sectional views of intermediate stages inthe manufacturing of the semiconductor device 100 in accordance withsome embodiments and FIG. 4 is a process flow diagram of the processshown in FIGS. 2A through 2G. With reference to FIG. 2A, there is shownthe semiconductor device 100 at an intermediate stage of processingincluding the contact layer 24, the dielectric layer 26, and an opening28. Although not shown in FIG. 2A, the contact layer 24 can be formedover or on the substrate 20 (step 302).

The contact layer 24 may include a doped region over the substrate 20.The contact layer may be formed of silicon, silicon germanium, siliconphosphide, silicon carbide, the like, or a combination thereof. Thecontact layer 24 may be epitaxially grown from the substrate 20 or fromsome other intermediate structure. In some embodiments, the contactlayer 24 is epitaxially grown in a recess formed in the substrate 20. Inother embodiments, the contact layer 24 is formed by doping a portion ofthe substrate 20 with an implantation process. For example, the contactlayer 24 may be a source region or a drain region of a transistor.

The dielectric layer 26 is formed over the contact layer 24 (step 304).The dielectric layer 26 may be formed of oxides such as silicon oxide,borophosphosilicate glass (BPSG), undoped silicate glass (USG),fluorinated silicate glass (FSG), low-k dielectrics such as carbon dopedoxides, extremely low-k dielectrics such as porous carbon doped silicondioxide, a polymer such as polyimide, the like, or a combinationthereof. The low-k dielectric materials may have k values lower than3.9. The dielectric layer 26 may be deposited by chemical vapordeposition (CVD), physical vapor deposition (PVD), atomic layerdeposition (ALD), a spin-on-dielectric (SOD) process, the like, or acombination thereof. In some embodiments, the dielectric layer 26 is aninter-layer dielectric (ILD).

After the dielectric layer 26 is formed, an opening 28 may be formedthrough the dielectric layer 26 to a top surface 24A of the contactlayer 24 (step 306). The opening 28 may be formed using acceptablephotolithography and etching techniques such as, for example, ananisotropic dry etch.

In some embodiments, the formation of the opening includes a maskingmaterial such as a photoresist. In these embodiments, the photoresist(not shown) may be deposited and patterned over the dielectric layer.The photoresist may comprise a conventional photoresist material, suchas a deep ultra-violet (DUV) photoresist, and may be deposited on thetop surface of the dielectric layer 26, for example, by using a spin-onprocess to place the photoresist. However, any other suitable materialor method of forming or placing the photoresist may alternatively beutilized. Once the photoresist has been formed, the photoresist may beexposed to energy, e.g. light, through a patterned reticle in order toinduce a reaction in those portions of the photoresist exposed to theenergy. The photoresist may then be developed, and portions of thephotoresist may be removed forming openings in the photoresist, exposingportions of a top surface of dielectric layer 26 through the openings.After the photoresist is patterned, the dielectric layer 26 may bepatterned to form the opening 28.

After the opening 28 is formed, an optional cleaning process may beperformed to remove the native oxide or any residue from the etchingprocess on the contact layer 24 (step 308). The cleaning process may beperformed using an HCl solution, and the cleaning time may be about oneminute, for example. In some embodiments, the native oxide can beavoided by maintaining the exposed contact layer 24 in a vacuum or in anoxygen or oxidizer free environment.

FIG. 2B illustrates forming a capping layer 30 over the dielectric layer26 and the contact layer 24 and in the opening 28 (step 310). In someembodiments, the capping layer 30 will be substantially consumed by thesubsequent process of forming the metal-silicide layer 40. The cappinglayer 30 can repair any damage to the contact layer 24 and thedielectric layer 26 caused by the etching of the opening 28. Inaddition, the capping layer 30 can increase the adhesion between thecontact structure 50 (see FIG. 2G) and the dielectric layer 26.

The capping layer 30 may be formed of silicon, germanium, silicongermanium, silicon carbide, silicon phosphide, the like, or acombination thereof. In some embodiments, the capping layer 30 has asubstantially same material composition as the contact layer. Forexample, in an embodiment where the contact layer 24 is formed ofsilicon germanium, the capping layer 30 is also formed of silicongermanium.

In an embodiment where the contact layer 24 is a part of an n-typemetal-oxide-semiconductor field-effect transistor (NMOS), the cappinglayer 30 is made of silicon, silicon phosphide, silicon carbide, thelike, or a combination thereof. In an embodiment where the contact layer24 is a part of a p-type metal-oxide-semiconductor field-effecttransistor (PMOS), the capping layer 30 is made of silicon, germanium,silicon germanium, the like, or a combination thereof. As illustrated inFIG. 2B, the capping layer 30 includes a portion 30A adjoining thecontact layer 24, portions 30B extending along sidewalls of the opening28 and adjoining the dielectric layer 26, and portions 30C extendingover and adjoining the dielectric layer 26. In some embodiments, thecapping layer 30 is formed by CVD, ALD, PVD, the like, or a combinationthereof to a thickness from about 10 Å to about 200 Å. The capping layer30 may be conformally deposited to have a substantially uniformthickness along the bottom and sidewalls of the opening 28 and over thedielectric layer 26.

After the capping layer 30 is formed, the metal layer 32 is formed overthe capping layer 30 and in the opening as illustrated in FIG. 2C (step312). In some embodiments, the metal layer 32 will be substantiallyconsumed by the subsequent process of forming the metal-silicide layer40. The metal layer 32 may be formed of nickel, cobalt, titanium,tungsten, the like, or a combination thereof. As illustrated in FIG. 2C,the metal layer 32 includes a portion 32A at the bottom of the opening,portions 32B extending along sidewalls of the opening, and portions 32Cextending over the dielectric layer 26. In some embodiments, the metallayer 32 is formed by PVD, ALD, sputter deposition, the like, or acombination thereof to a thickness from about 30 Å to about 300 Å. Themetal layer 32 may be conformally deposited to have a substantiallyuniform thickness along the bottom and sidewalls of the opening and overthe dielectric layer 26.

After the metal layer 32 is formed, the glue layer 34 is formed over themetal layer 32 and in the opening as illustrated in FIG. 2D (step 314).The glue layer 34 improves the adhesion between the subsequently formedconductive plug 42′ (see FIG. 2G) and also prevents oxidation of themetal layer 32. The glue layer 34 may be formed of titanium nitride,tantalum nitride, the like, or a combination thereof. As illustrated inFIG. 2D, the glue layer 34 includes a portion 34A at the bottom of theopening, portions 34B extending along sidewalls of the opening, andportions 34C extending over the dielectric layer 26. In someembodiments, the glue layer 34 is formed by CVD, PVD, ALD, the like, ora combination thereof to a thickness from about 5 Å to about 50 Å. Theglue layer 34 may be conformally deposited to have a substantiallyuniform thickness along the bottom and sidewalls of the opening and overthe dielectric layer 26.

FIG. 2E illustrates the silicidation process to form the metal-silicidelayer 40 from the capping layer 30 and the metal layer 32 (step 316).The formation of the metal-silicide layer 40 includes performing anannealing process on the semiconductor device 100. The annealing processcauses the capping layer 30 to react with the metal layer 32 to form themetal-silicide layer 40. In some embodiments, the annealing process isperformed using thermal soaking, spike annealing, flash annealing, laserannealing, the like, or a combination thereof. In some embodiments, theannealing process is performed at a temperature from about 100° C. toabout 900° C., in an atmosphere including process gases such as Ar, N₂,the like, or a combination thereof, and at a pressure from 770 Torr toabout 1000 Torr.

After the metal-silicide layer 40 is formed, in some embodiments, thereremains an unreacted metal layer 32′ that was not converted into themetal-silicide layer 40. As illustrated in FIG. 2E, the metal-silicidelayer 40 includes a portion 40A at the bottom of the opening andadjoining the contact layer 24, portions 40B extending along sidewallsof the opening and adjoining the dielectric layer 26, and portions 40Cextending over and adjoining the dielectric layer 26. In someembodiments, the bottom portion 40A of the metal-silicide layer 40 has athickness from about 30 Å to about 300 Å, and the sidewall portions 40Bof the metal-silicide layer 40 has a thickness from about 3 Å to about30 Å.

FIG. 2F illustrates filling the opening in the dielectric layer 26 withthe conductive material 42 (step 318). In some embodiments, theconductive material 42 fills the opening and also extends over thedielectric layer 26. The conductive material 42 will form thesubsequently formed conductive plug 42′ (see FIG. 2G). In someembodiments, the conductive material 42 is formed of tungsten. Inalternative embodiments, the conductive material 42 includes othermetal(s) or metal alloys such as aluminum, copper, titanium nitride,tantalum nitride, the like, or a combination thereof. The formation ofthe conductive material may be performed using CVD, ALD, PVD,sputtering, the like, or a combination thereof.

In the embodiments where the conductive material 42 extends over thedielectric layer 26, a planarization process may be performed on theconductive material 42 to form the conductive plug 42′ as illustrated inFIG. 2G (step 320). In some embodiments, the planarization process is achemical mechanical polishing (CMP) process, an etching process, thelike, or a combination thereof. After the planarization process, the topsurface 42A of the conductive plug 42′ is substantially coplanar withthe top surface 26A of the dielectric layer 26. As illustrated in FIG.2G, the metal-silicide layer 40, the unreacted metal layer 32′ (ifpresent), the glue layer 34, and the conductive plug 42′ forms thecontact structure 50.

FIG. 3 illustrates a cross-sectional view of a semiconductor device 200in accordance with some embodiments. The semiconductor device 200includes an active device 150 formed on a substrate 202. In theillustrated embodiment, the active device 150 is a transistor, althoughother embodiments may include various other active and passive devicessuch as resistors, capacitors, inductors, diodes, varactors, the like,or a combination thereof. In an embodiment, the active device 150 is afin field-effect transistor (FinFET).

The substrate 202 may be a part of a wafer and may include asemiconductor material such as silicon, germanium, diamond, or the like.Alternatively, compound materials such as silicon germanium, siliconcarbide, gallium arsenic, indium arsenide, indium phosphide, silicongermanium carbide, gallium arsenic phosphide, gallium indium phosphide,combinations of these, and the like, may also be used. Additionally, thesubstrate 202 may comprise a SOI substrate. Generally, an SOI substratecomprises a layer of a semiconductor material such as epitaxial silicon,germanium, silicon germanium, SOI, SGOI, or combinations thereof. Thesubstrate 202 may be doped with a p-type dopant, such as boron,aluminum, gallium, or the like, although the substrate may alternativelybe doped with an n-type dopant, as is known in the art. Only a portionof the substrate 202 is illustrated in the figures, as this issufficient to fully describe this illustrative embodiment. In someembodiments, the substrate 202 is a semiconductor fin extending from asubstrate.

The active device 150 includes source/drain regions 210, a gatedielectric 204, a gate electrode 206, gate spacers 208, a dielectriclayer 212, and contact structures 50. The formation of the active device150 may begin with the formation of a gate dielectric layer (not shown)and a gate electrode layer (not shown). The gate dielectric layer may beformed by thermal oxidation, CVD, sputtering, or any other suitablemethods for forming a gate dielectric. In other embodiments, the gatedielectric layer includes dielectric materials having a high dielectricconstant (k value), for example, greater than 3.9. The materials mayinclude silicon nitrides, oxynitrides, metal oxides such as HfO₂,HfZrO_(x), HfSiO_(x), HfTiO_(x), HfAlO_(x), and the like, andcombinations and multi-layers thereof. In another embodiment, the gatedielectric layer may have a capping layer selected from metal nitridematerials such as titanium nitride, tantalum nitride, or molybdenumnitride.

The gate electrode layer (not shown) may be formed over the gatedielectric layer. The gate electrode layer may include a conductivematerial and may be selected from a group comprising ofpolycrystalline-silicon (poly-Si), poly-crystalline silicon-germanium(poly-SiGe), metal-nitrides, metal-silicides, metal-oxides, and metals.Examples of metal-nitrides include tungsten nitride, molybdenum nitride,titanium nitride, and tantalum nitride, the like, or a combinationthereof. Examples of metal-silicides include tungsten silicide, titaniumsilicide, cobalt silicide, nickel silicide, platinum silicide, erbiumsilicide, the like, or a combination thereof. Examples of metal-oxidesinclude ruthenium oxide, indium tin oxide, the like, or a combinationthereof. Examples of metals include tungsten, titanium, aluminum,copper, molybdenum, nickel, platinum, the like, or a combinationthereof.

The gate electrode layer may be deposited by CVD, sputter deposition, orother suitable techniques for depositing conductive materials. Thethickness of the gate electrode layer may be in the range of about 200 Åto about 4,000 Å. The top surface of the gate electrode layer usuallyhas a non-planar top surface, and may be planarized, for example by aCMP process; prior to patterning of the gate electrode layer or gateetch. Ions may or may not be introduced into the gate electrode layer atthis point, for example, by ion implantation techniques.

After the gate electrode layer is formed, the gate electrode layer andthe gate dielectric layer may be patterned to form the gate electrode206 and the gate dielectric 204. The gate patterning process may includedepositing and patterning a gate mask (not shown) on the gate electrodelayer using acceptable deposition and photolithography techniques. Thegate mask may incorporate commonly used masking materials, such as (butnot limited to) photoresist material, silicon oxide, silicon oxynitride,and/or silicon nitride. The gate electrode layer and the gate dielectriclayer may be etched using plasma etching to form the gate electrode 206and the gate dielectric 204 as illustrated in FIG. 3.

After the gate electrode 206 and the gate dielectric 204 are formed, thesource/drain regions 210 may be formed. The source/drain regions 210 maybe formed by doping portions of the substrate 202 with an implantationprocess to implant appropriate dopants to complement the dopants in thesubstrate 202. In an embodiment where the substrate 202 is implantedwith p-type dopants such as boron, gallium, indium, or the like, thesource/drain regions 210 are implanted with n-type dopants such asphosphorous, arsenic, antimony, or the like. The source/drain regions210 may be implanted using the gate electrode 206 as a mask. In someembodiments, the doped source/drain regions 210 may be annealed topromote diffusion of the dopant impurities into the substrate 202.

In another embodiment, the source/drain regions 210 may be formed byforming recesses (not shown) in substrate 202 and epitaxially growingmaterial in the recesses. In an embodiment, the recesses may be formedby an anisotropic etch. Alternatively, the recesses may be formed by anisotropic orientation dependent etching process, whereintetramethylammonium hydroxide (TMAH) or the like may be used as anetchant. After the recesses are formed, the source/drain regions 210 maybe formed by epitaxially growing material in the recesses. During theepitaxy process, etching gas, such as HCl gas, may be added (as anetching gas) into the process gas, so that the source/drain regions 210are selectively grown in the recesses, but not on the gate electrode206. In alternative embodiments, no etching gas is added, or the amountof etching gas is small, so that there is a thin layer of thesource/drain regions 210 formed on the substrate 202 and the gateelectrode 206. In yet another embodiment, the gate electrode 206 and thesubstrate 202 could be covered with a sacrificial layer (not shown) toprevent epitaxial growth thereon. The source/drain regions 210 may bedoped either through an implantation method as discussed above, or elseby in-situ doping as the material is grown.

The formation methods of the source/drain regions 210 may include ALD,CVD, such as a reduced pressure CVD (RPCVD), metalorganic chemical vapordeposition (MOCVD), or other applicable methods. Depending on thedesirable composition of the source/drain regions 210, the precursorsfor the epitaxial growth may include SiH₄, GeH₄, CH₃, PH₃, and/or thelike, and the partial pressures of the Si-containing gases,Ge-containing gases, C-containing gases, and P-containing gases areadjusted to modify the atomic ratio of germanium/carbon/phosphorous tosilicon.

In some embodiments the source/drain regions 210 are formed so as toimpart a strain on the channel region underneath the gate electrode 206.In an embodiment where the substrate 202 is formed of silicon, thesource/drain regions 210 may then be formed through a selectiveepitaxial growth (SEG) process with a material, such as silicongermanium, silicon carbon, or the like that has a different latticeconstant than the silicon. The lattice mismatch between the stressormaterial in the source/drain regions 210 and the channel region formedunderneath the gate electrode 206 will impart a stress into the channelregion that will increase the carrier mobility and the overallperformance of the device. The source/drain regions 210 may be dopedeither through an implantation method as discussed above, or else byin-situ doping as the material is grown.

The gate spacers 208 may be formed by blanket depositing a spacer layer(not shown) over the gate electrode 206 and the substrate 202. Thespacer layer may comprise of SiN, oxynitride, SiC, SiON, oxide, and thelike and may be formed by methods utilized to form such a layer, such asCVD, plasma enhanced CVD, sputtering deposition, the like, or acombination thereof. The gate spacers 208 are then patterned, preferablyby anisotropically etching to remove the spacer layer from thehorizontal surfaces of the gate electrode 206 and the substrate 202.

In some embodiments, the source/drain regions 210 include lightly dopedregions (not shown) and heavily doped regions. In this embodiment,before the gate spacers 208 are formed, the source/drain regions 210 maybe lightly doped. After the gate spacers 208 are formed, thesource/drain regions 210 may then be heavily doped. This forms lightlydoped regions and heavily doped regions. The lightly doped regions areprimarily underneath the gate spacers 208 while the heavily dopedregions are outside of the gate spacers 208 along the substrate 202.

After the formation of the gate electrode 206, the source/drains 210,and the gate spacers 208, the dielectric layer 212 is formed. Thedielectric layer 212 may be formed of oxides such as silicon oxide,BPSG, USG, FSG, low-k dielectrics such as carbon doped oxides, extremelylow-k dielectrics such as porous carbon doped silicon dioxide, a polymersuch as polyimide, the like, or a combination thereof. The low-kdielectric materials may have k values lower than 3.9. The dielectriclayer 26 may be deposited by CVD, PVD, ALD, an SOD process, the like, ora combination thereof. The dielectric layer 212 may also be referred toas ILD 212.

After the dielectric layer 212 is formed, openings (not shown) areformed through the dielectric layer 212 to expose a portion of thesource/drains 210. The openings may be formed using acceptablephotolithography and etching techniques such as, for example, ananisotropic dry etch.

After the openings are formed in the dielectric layer 212, the contactstructures 50 are formed in the openings. The contact structures 50 areformed in a similar manner as described above in FIGS. 2A through 2G andthe description is not repeated herein. The contact structures 50electrically couple the source/drain regions 210 to overlying structures(not shown) such as conductive lines/vias and/or other active andpassive devices. For example, an interconnect structure includealternating layers of dielectric material and conductive material may beformed over the contact structures 50 and the dielectric layer 212. Thecontact structures 50 can electrically couple the source/drain regions210 to this interconnect structure.

According to embodiments of the present disclosure, advantages include alow resistance silicide contact with improved process stability. Inparticular, the present disclosure forms the silicide in the contactopening after the contact opening is formed rather than forming thesilicide before the contact is formed. In this process, a capping layeris formed inside the contact opening and a metal layer is formed overthe capping layer. These layers are then annealed to form the silicidelayer. By forming the capping layer after the contact opening is formed,the capping layer properties are not affected by the contact openingetching process, the dielectric layer formation, or any other processesperformed before the capping layer formation. This improves theprocessing window for the capping layer formation and also improves theprocess stability for the contact formation. In addition, the cappinglayer can repair damage caused by the etching of the contact opening.

An embodiment is a method of forming a semiconductor device, the methodincluding forming a contact region over a substrate, forming adielectric layer over the contact region and the substrate, and formingan opening through the dielectric layer to expose a portion of thecontact region. The method further includes forming a metal-silicidelayer on the exposed portion of the contact region and along sidewallsof the opening, and filling the opening with a conductive material toform a conductive plug in the dielectric layer, the conductive plugbeing electrically coupled to the contact region.

Another embodiment is method of forming a contact structure, the methodincluding forming a contact layer over a substrate, depositing adielectric layer over the contact layer and the substrate, patterningthe dielectric layer to form an opening through the dielectric layer, atleast a portion of the contact layer being exposed in the opening, anddepositing a capping layer in the opening along the exposed contactlayer and sidewalls of the dielectric layer and over the dielectriclayer. The method further includes depositing a metal layer on thecapping layer in the opening and over the dielectric layer, depositing aglue layer on the metal layer in the opening and over the dielectriclayer, and after depositing the glue layer, annealing the capping layerand the metal layer to form a metal-silicide layer in the opening alongthe contact layer and the sidewalls of the dielectric layer and over thedielectric layer.

A further embodiment is a method of forming a contact structure, themethod including forming a contact region in a substrate, forming adielectric layer over the contact region, forming an opening in thedielectric layer to expose at least a surface of the contact region, andconformally depositing a silicon-containing capping layer along theexposed surface of the contact region and sidewalls of the opening. Themethod further includes conformally depositing a metal layer on thesilicon-containing capping in the opening, conformally depositing a gluelayer on the metal layer in the opening, and annealing thesilicon-containing capping layer and the metal layer to form ametal-silicide layer in the opening along the contact region and thesidewalls of the dielectric layer.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: forming a contact region ona substrate; forming a dielectric layer over the contact region and thesubstrate; forming an opening through the dielectric layer to expose aportion of the contact region; forming a silicon-containing cappinglayer along the exposed portion of the contact region, sidewalls of theopening, and over the dielectric layer; forming a metal layer over thesilicon-containing capping layer in the opening and over the dielectriclayer; performing a silicidation process to react at least portions ofthe silicon-containing capping layer and the metal layer to form ametal-silicide layer on the exposed portion of the contact region andalong sidewalls of the opening, the silicidation process consuming atleast a portion of the contact region; and filling the opening over themetal-silicide layer with a conductive material to form a conductiveplug in the dielectric layer, the conductive plug being electricallycoupled to the contact region.
 2. The method of claim 1 furthercomprising: planarizing the conductive material to form the conductiveplug, wherein after the planarizing step a top surface of the conductiveplug is coplanar with a top surface of the dielectric layer.
 3. Themethod of claim 1, where the substrate is a semiconductor fin for a finfield-effect transistor (FinFET) and the contact region is asource/drain region for the FinFET, and wherein the forming the contactregion comprises: etching a recess in semiconductor fin; epitaxiallygrowing a semiconductor material in the recess; and doping thesemiconductor material with at least one dopant to form a source/drainregion.
 4. The method of claim 1, wherein the contact region comprisessilicon, silicon germanium, silicon phosphide, silicon carbide, or acombination thereof.
 5. The method of claim 1, wherein thesilicon-containing capping layer comprises silicon, germanium, silicongermanium, silicon carbide, silicon phosphide, or a combination thereof.6. The method of claim 1, wherein the metal layer comprises nickel,cobalt, titanium, tungsten, or a combination thereof.
 7. The method ofclaim 1, wherein the metal-silicide layer extends along the sidewalls ofthe opening from a top surface of the contact region to a top surface ofthe dielectric layer.
 8. The method of claim 1, wherein themetal-silicide layer has a first thickness along the contact region anda second thickness along the sidewalls of the opening, the firstthickness being greater than the second thickness.
 9. The method ofclaim 8, wherein the first thickness is from about 30 Angstroms (Å) toabout 300 Å and the second thickness is from about 3 Å to about 30 Å.10. The method of claim 1 further comprising: before performing thesilicidation process, forming a glue layer over the metal layer in theopening and over the dielectric layer.
 11. The method of claim 1,wherein the silicon-containing capping layer has a same materialcomposition as the contact region.
 12. A method comprising: forming asource/drain region of a field-effect transistor (FET) on asemiconductor substrate; depositing a dielectric layer over thesource/drain region and the semiconductor substrate; patterning thedielectric layer to form an opening through the dielectric layer, atleast a portion of the source/drain region being exposed in the opening;depositing a capping layer in the opening along the exposed portion ofthe source/drain region and sidewalls of the dielectric layer and overthe dielectric layer; depositing a metal layer over the capping layer inthe opening and over the dielectric layer; annealing the capping layerand the metal layer to form a metal-silicide layer in the opening alongthe source/drain region and the sidewalls of the dielectric layer andover the dielectric layer; and after forming the metal-silicide layer,filling a conductive material over metal-silicide layer in the openingand over the dielectric layer.
 13. The method of claim 12, wherein theforming the source/drain region comprises: etching a recess in thesemiconductor substrate; epitaxially growing a semiconductor material inthe recess; and doping the semiconductor material with at least onedopant to form the source/drain region.
 14. The method of claim 12further comprising: before annealing the capping layer and the metallayer, forming a glue layer over the metal layer in the opening and overthe dielectric layer.
 15. A method comprising: forming a dielectriclayer over a substrate; forming an opening in the dielectric layer toexpose a first portion of a surface of the substrate; depositing asilicon-containing capping layer along the exposed first portion of thesurface of the substrate and sidewalls of the opening; depositing ametal layer over the silicon-containing capping layer in the opening;depositing a glue layer over the metal layer in the opening; afterdepositing the glue layer, annealing the silicon-containing cappinglayer and the metal layer to form a metal-silicide layer in the openingalong the first portion of the surface of the substrate and thesidewalls of the dielectric layer; and filling a conductive material inthe opening over the glue layer and over the dielectric layer.
 16. Themethod of claim 15, wherein after the annealing the silicon-containingcapping layer and the metal layer to form the metal-silicide layer, aportion of the metal layer remains unreacted and is interposed betweenthe metal-silicide layer and the glue layer.
 17. The method of claim 15,wherein the silicon-containing capping layer has a same materialcomposition as the first portion of the surface of the substrate. 18.The method of claim 15, wherein the metal-silicide layer has a surfaceextending below a topmost surface of the substrate.
 19. The method ofclaim 15, wherein the silicon-containing capping layer comprisessilicon, germanium, silicon germanium, silicon carbide, siliconphosphide, or a combination thereof.
 20. The method of claim 15, whereinthe glue layer comprises titanium nitride, tantalum nitride, or acombination thereof.